The correct option is C a lilting love lyric
The poem here seems like an elaborate compliment to the woman, Juliana, with whom the mower has fallen in love- the entire poem revolves around how the glowworms are powerful and beautiful but they are nothing compared to Juliana. The rhyme scheme and rhythm here support the poet in this endeavor. So, it would be correct to assume that the poetic rhythm serves to convey to the reader "a lilting love lyric." The mower does not make any emotional plea so the rhythm cannot possibly convey that and it neither conveys a sense of loss nor does it carry a weighty message. So, the answer is option C.